Michelle Nokken

Effect of surface treatment on the post-peak residual strength and toughness of polypropylene/polyethylene-blended fiber-reinforced concrete

This study involved an experimental investigation into the improvement of mechanical properties of fiber-reinforced concrete (FRC) utilizing chemically treated polypropylene/polyethylene fibers. Four types of chemical surface treatments were examined: two types of chromic acid (Types B and C), potassium permanganate (PP), and hydrogen peroxide solutions. Untreated and treated fibers were added at 0.32% by volume of concrete and also at 0.50% for the best treatment technique. Compressive and flexural strength were measured to quantify improvement. It was found that there were no significant differences in compressive strength. Type B chromic acid solution was found to be the most effective technique in improving the flexural strength of FRC resulting in average increases of 8.9% and 17.6% for peak and residual strengths, respectively, compared to nontreated fibers. While not as effective as plasma treatments, further research may be warranted for chemical treatments. Surface wettability of the treated fibers was measured by contact angle with water. The contact angle was found to have no correlation to the toughness. The higher volume of fibers, both treated and nontreated gave higher residual strength and toughness; however, surface treatment did not significantly enhance mechanical properties.

MEASURED INTERNAL TEMPERATURES IN CONCRETE EXPOSED TO OUTDOOR CYCLIC FREEZING

In this paper, temperature data collected by thermocouples embedded into concrete over a period of 10 years are analyzed for a concrete slab and beam located outdoors near Kingston, Ontario. Temperatures measured in the concrete are compared with temperatures encountered in ASTM C 666 Resistance of Concrete to Rapid Freezing and Thawing and ASTM C 1293 Standard Test Method for Concrete Aggregates by Determination of Length Change of Concrete Due to Alkali-Silica Reaction. The average number of freezing and thawing cycles at the site was counted using different freezing and thawing temperature criteria as presented in the literature by various authors. Results are compared with data from a second site. The rates of freezing and thawing occurring at the outdoor exposure site were found to be significantly less than specified in the ASTM C 666 laboratory test. Average daily maximum temperatures in July were at approximately 33°C at depths of 50 mm in the concrete.

Effects of Temperature, Chemical, and Mineral Admixtures on the Electrical Conductivity of Concrete

ASTM C1202 has become a very common test method for prequalification purposes and for performance-based specifications in North America. Although the test neither directly determines the permeability or chloride resistance, it has often been shown to have good correlation to those properties since electrical conductivity is also related to the porosity and connectivity of the pore structure. The prevalence of the test is largely based on its ease of execution and its wide acceptance and use by many state and provincial DOTs. More recently, ASTM subcommittee C09.66 has discussed replacing the above test method with a more rapid method measuring conductivity. Several factors affect the conductivity of concrete, mixture design, inclusion of chemical and mineral admixtures, the temperature during testing and the age or maturity at test time. Research was carried out to investigate the magnitude of these variables on measured conductivity. Conductivity was measured using the same equipment as the ASTM C1202 method with changes in the magnitude and duration of the applied voltage as well as the solutions used in the test cell chamber. Conductivity was measured every three hours starting at one day after casting until seven days and weekly until 28 days. Conductivity was found to decrease with hydration as expected. It was determined that mixture design and temperature have significant effects on measured conductivity while chemical admixtures have less influence with the exception of corrosion inhibitors. The developed test method presents potential as a tool for prequalification and quality control that can be directly related to maturity and durability.

An Experimental Study on the Effective Parameters of Thermal Conductivity of Mine Backfill

This paper investigates the thermal conductivity of cemented backfill. Two major measurement methods, namely, steady state and unsteady state, are compared. Effect of backfill design parameters such as pulp density and binder content, along with sample homogeneity and sample size, are studied. Thermal conductivity of backfill with and without sodium silicate additive, as a new binder, is investigated. A novel method for interpreting thermal conductivity of backfill is presented by introducing backfill as a multiphase porous material for which the effects of physical parameters, such as degree of saturation, porosity, and thermal conductivity of solid particles, are studied. The results of this research help to better understand the thermal interaction of backfill with the surrounding rock mass and therefore contribute to progressive improvement of backfill technology.

Development of In Situ Water Absorption Method: Laboratory Study and Field Validation

AbstractConcrete porosity and its interconnection are crucial aspects that influence durability. Taking into account that moisture is required for many concrete deterioration processes, water absor...

Effect of UV and UV–Ozone Treatment of Polyolefin Fibers on Toughness of Fiber Concrete Composite

Ultraviolet (UV) irradiation and a combination of UV irradiation and ozone treatment of polyolefin fibers were investigated for possible improvement of mechanical properties in concrete composites. In both treatment methods, various fiber exposure durations were used, and surface modification was monitored by measuring the water contact angle. Untreated and treated fibers were added to concrete at 0.32 % by volume, and the specimens were tested for flexural strength according to ASTM International specifications. Fiber surface treatment by UV alone was found to be an unattractive technique based on the results of flexural tests and contact angle measurements. Ten minutes of UV and ozone surface treatment of fibers was found to improve the composite peak stress by 11 % and the toughness by 4 %; longer periods of exposure led to lower flexural strength results, perhaps as a result of fiber deformation or degradation.